144 



Part III. — Eighteenth Annual Report 



III. — NOTES ON SOME CRUSTACEAN PARASITES OF FISHES. 

 By Thomas Scott, F.L.S., Mem. Zool. Soc. de France. 



Plates V.-VIII. 

 Contents. 



page. 



Introductory Note, ........ 144 



Copepod-Parasites of Fishes — Ergasilidae, ..... 146 



„ ,, ,, — Caligidte, . . . . .147 



,, ,, — Dichelestidae, ..... 159 



,, ,, — Lernaeidse, ..... 160 



,, ,, ,, — Chondracanthidae, .... 163 



,, ,, ,, — Lernaeopodidae, ..... 169 



Branchiura, . . . . . . . . .179 



Isopoda parasita, . . . . . . . .180 



Amphipoda parasita, . . . . . , . .180 



List of Fishes on which Parasites have been found, .... 181 



Concluding Remarks, ........ 182 



Description of the Plates, . . . . . . .183 



INTRODUCTORY NOTE. 



Parasitic habits are not restricted or peculiar to any particular class of 

 organisms, but may be found more or less in evidence in all departments 

 both of the animal and vegetable kingdoms. There are, however, certain 

 groups of plants and animals whose surroundings and conditions of life 

 seem to be specially favourable to the adoption of parasitic habits, and 

 amongst the Crustacea such habits seem to prevail to a considerable 

 extent, especially amongst the so-called "lower forms" belonging to that 

 class. 



Different kinds of animals have to act the part of hosts to these 

 parasitic crustaceans, and the animals which are called upon to willingly, 

 or unwillingly, act this part belong chiefly to the same class to which the 

 parasites themselves belong and to the fishes. Fishes appear to be special 

 favourites in this respect. Scarcely any part of a fish's body is free from 

 the intrusion of these unwelcome or (in some cases, perhaps) welcome 

 visitors \ they are found running over the skin of the fish, they adhere 

 to the fins, the gills and gill covers, they are found ou the lips, the 

 tongue, and the roof and sides of the throat, in the nasal fossae, and in 

 other and even more strange and out-of-the-way places ou or about the 

 body of the fish. 



The degree of parasitism varies greatly even amongst closely-allied 

 species ; in some cases the relationship of the crustacean to the fish is 

 decidedly that of a parasite, but in other cases it would be inaccurate to 

 describe the association of the one with the other as truly parasitic. Some- 

 times, however, it is more convenient to use the terms 'parasitic, parasite, 

 etc., in this broad sense, even though it may not in some cases be strictly 

 correct, in order to avoid the complications that would arise by any 

 attempt to describe, in a strictly accurate manner, the various degrees of 

 relationships that exist between crustaceans and the fishes which have 

 become their hosts ; it is in this wider sense that such terms are used in 

 the present paper. 



The study of the parasitic Crustacea is in some respects more difficult, 

 if also more interesting, than that of the species which live under normal 



